Shane Lindsay

Lexical Integration of Novel Words without Sleep.

Learning a new word involves integration with existing lexical knowledge. Previous work has shown that sleep-associated memory consolidation processes are important for the engagement of novel items in lexical competition. In 3 experiments we used spaced exposure regimes to investigate memory for novel words and whether lexical integration can occur within a single day. The degree to which a new spoken word (e.g., cathedruke) engaged in lexical competition with established phonological neighbors (e.g., cathedral) was employed as a marker for lexical integration. We found evidence for improvements in recognition and cued recall following a time period including sleep, but we also found lexical competition effects emerging within a single day. Spaced exposure to novel words on its own did not bring about this within-day lexical competition effect (Experiment 2), which instead occurred with either spaced or massed exposure to novel words, provided that there was also spaced exposure to the phonological neighbors (Experiments 1 and 3). Although previous studies have indicated that sleep-dependent memory consolidation may be sufficient for lexical integration, our results show it is not a necessary precondition.

The selective role of premotor cortex in speech perception: A contribution to phoneme judgements but not speech comprehension

Several accounts of speech perception propose that the areas involved in producing language are also involved in perceiving it. In line with this view, neuroimaging studies show activation of premotor cortex (PMC) during phoneme judgment tasks; however, there is debate about whether speech perception necessarily involves motor processes, across all task contexts, or whether the contribution of PMC is restricted to tasks requiring explicit phoneme awareness. Some aspects of speech processing, such as mapping sounds onto meaning, may proceed without the involvement of motor speech areas if PMC specifically contributes to the manipulation and categorical perception of phonemes. We applied TMS to three sites—PMC, posterior superior temporal gyrus, and occipital pole—and for the first time within the TMS literature, directly contrasted two speech perception tasks that required explicit phoneme decisions and mapping of speech sounds onto semantic categories, respectively. TMS to PMC disrupted explicit phonological judgments but not access to meaning for the same speech stimuli. TMS to two further sites confirmed that this pattern was site specific and did not reflect a generic difference in the susceptibility of our experimental tasks to TMS: stimulation of pSTG, a site involved in auditory processing, disrupted performance in both language tasks, whereas stimulation of occipital pole had no effect on performance in either task. These findings demonstrate that, although PMC is important for explicit phonological judgments, crucially, PMC is not necessary for mapping speech onto meanings.

Sleep Underpins the Plasticity of Language Production

The constraints that govern acceptable phoneme combinations in speech perception and production have considerable plasticity. We addressed whether sleep influences the acquisition of new constraints and their integration into the speech-production system. Participants repeated sequences of syllables in which two phonemes were artificially restricted to syllable onset or syllable coda, depending on the vowel in that sequence. After 48 sequences, participants either had a 90-min nap or remained awake. Participants then repeated 96 sequences so implicit constraint learning could be examined, and then were tested for constraint generalization in a forced-choice task. The sleep group, but not the wake group, produced speech errors at test that were consistent with restrictions on the placement of phonemes in training. Furthermore, only the sleep group generalized their learning to new materials. Polysomnography data showed that implicit constraint learning was associated with slow-wave sleep. These results show that sleep facilitates the integration of new linguistic knowledge with existing production constraints. These data have relevance for systems-consolidation models of sleep.

The benefits of targeted memory reactivation for consolidation in sleep are contingent on memory accuracy and direct cue-memory associations

STUDY OBJECTIVES To investigate how the effects of targeted memory reactivation (TMR) are influenced by memory accuracy prior to sleep and the presence or absence of direct cue-memory associations. METHODS 30 participants associated each of 50 pictures with an unrelated word and then with a screen location in two separate tasks. During picture-location training, each picture was also presented with a semantically related sound. The sounds were therefore directly associated with the picture locations but indirectly associated with the words. During a subsequent nap, half of the sounds were replayed in slow wave sleep (SWS). The effect of TMR on memory for the picture locations (direct cue-memory associations) and picture-word pairs (indirect cue-memory associations) was then examined. RESULTS TMR reduced overall memory decay for recall of picture locations. Further analyses revealed a benefit of TMR for picture locations recalled with a low degree of accuracy prior to sleep, but not those recalled with a high degree of accuracy. The benefit of TMR for low accuracy memories was predicted by time spent in SWS. There was no benefit of TMR for memory of the picture-word pairs, irrespective of memory accuracy prior to sleep. CONCLUSIONS TMR provides the greatest benefit to memories recalled with a low degree of accuracy prior to sleep. The memory benefits of TMR may also be contingent on direct cue-memory associations.

Markers of automaticity in sleep-associated consolidation of novel words.

Two experiments investigated effects of sleep on consolidation and integration of novel form-meaning mappings using size congruity and semantic distance paradigms. Both paradigms have been used in previous studies to measure automatic access to word meanings. When participants compare semantic or physical font size of written word-pairs (e.g. BEE-COW), judgments are typically faster if relative sizes are congruent across both dimensions. Semantic distance effects are also found for wellestablished words, with semantic size judgements faster for pairs that differ substantially on this dimension. English-speaking participants learned novel form-meaning mappings with Mandarin (Experiment 1) or Malay (Experiment 2) words and were tested following overnight sleep or a similar duration awake. Judgements on English words controlled for circadian effects. The sleep group demonstrated selective stronger size congruity and semantic distance effects for novel word-pairs. This benefit occurred in Experiment 1 for semantic size comparisons of novel words, and in Experiment 2 on comparisons where novel pairs had large distances and font differences (for congruity effects) or in congruent trials (for semantic distance effects). Conversely, these effects were equivalent across sleep and wake for English words. Experiment 2 included polysomnography data and revealed that changes in the strength of semantic distance and congruity effects were positively correlated with slow-wave sleep and sleep spindles respectively. These findings support systems consolidation accounts of declarative learning and suggest that sleep plays an active role in integrating new words with existing knowledge, resulting in increased automatic access of the acquired knowledge.

To Dash or to Dawdle: Verb-Associated Speed of Motion Influences Eye Movements during Spoken Sentence Comprehension

In describing motion events verbs of manner provide information about the speed of agents or objects in those events. We used eye tracking to investigate how inferences about this verb-associated speed of motion would influence the time course of attention to a visual scene that matched an event described in language. Eye movements were recorded as participants heard spoken sentences with verbs that implied a fast (“dash”) or slow (“dawdle”) movement of an agent towards a goal. These sentences were heard whilst participants concurrently looked at scenes depicting the agent and a path which led to the goal object. Our results indicate a mapping of events onto the visual scene consistent with participants mentally simulating the movement of the agent along the path towards the goal: when the verb implies a slow manner of motion, participants look more often and longer along the path to the goal; when the verb implies a fast manner of motion, participants tend to look earlier at the goal and less on the path. These results reveal that event comprehension in the presence of a visual world involves establishing and dynamically updating the locations of entities in response to linguistic descriptions of events.

Mechanisms of Memory Retrieval in Slow-Wave Sleep

Abstract Study Objectives Memories are strengthened during sleep. The benefits of sleep for memory can be enhanced by re-exposing the sleeping brain to auditory cues; a technique known as targeted memory reactivation (TMR). Prior studies have not assessed the nature of the retrieval mechanisms underpinning TMR: the matching process between auditory stimuli encountered during sleep and previously encoded memories. We carried out two experiments to address this issue. Methods In Experiment 1, participants associated words with verbal and nonverbal auditory stimuli before an overnight interval in which subsets of these stimuli were replayed in slow-wave sleep. We repeated this paradigm in Experiment 2 with the single difference that the gender of the verbal auditory stimuli was switched between learning and sleep. Results In Experiment 1, forgetting of cued (vs. noncued) associations was reduced by TMR with verbal and nonverbal cues to similar extents. In Experiment 2, TMR with identical nonverbal cues reduced forgetting of cued (vs. noncued) associations, replicating Experiment 1. However, TMR with nonidentical verbal cues reduced forgetting of both cued and noncued associations. Conclusions These experiments suggest that the memory effects of TMR are influenced by the acoustic overlap between stimuli delivered at training and sleep. Our findings hint at the existence of two processing routes for memory retrieval during sleep. Whereas TMR with acoustically identical cues may reactivate individual associations via simple episodic matching, TMR with nonidentical verbal cues may utilize linguistic decoding mechanisms, resulting in widespread reactivation across a broad category of memories.

Event processing in the visual world: Projected motion paths during spoken sentence comprehension

Motion events in language describe the movement of an entity to another location along a path. In 2 eye-tracking experiments, we found that comprehension of motion events involves the online construction of a spatial mental model that integrates language with the visual world. In Experiment 1, participants listened to sentences describing the movement of an agent to a goal while viewing visual scenes depicting the agent, goal, and empty space in between. Crucially, verbs suggested either upward (e.g., jump) or downward (e.g., crawl) paths. We found that in the rare event of fixating the empty space between the agent and goal, visual attention was biased upward or downward in line with the verb. In Experiment 2, visual scenes depicted a central obstruction, which imposed further constraints on the paths and increased the likelihood of fixating the empty space between the agent and goal. The results from this experiment corroborated and refined the previous findings. Specifically, eye-movement effects started immediately after hearing the verb and were in line with data from an additional mouse-tracking task that encouraged a more explicit spatial reenactment of the motion event. In revealing how event comprehension operates in the visual world, these findings suggest a mental simulation process whereby spatial details of motion events are mapped onto the world through visual attention. The strength and detectability of such effects in overt eye-movements is constrained by the visual world and the fact that perceivers rarely fixate regions of empty space.

A Prerequisite to L1 Homophone Effects in L2 Spoken-Word Recognition.

When both members of a phonemic contrast in L2 (second language) are perceptually mapped to a single phoneme in one’s L1 (first language), L2 words containing a member of that contrast can spuriously activate L2 words in spoken-word recognition. For example, upon hearing cattle, Dutch speakers of English are reported to experience activation of kettle, as L1 Dutch speakers perceptually map the vowel in the two English words to a single vowel phoneme in their L1. In an auditory word-learning experiment using Greek and Japanese speakers of English, we asked whether such cross-lexical activation in L2 spoken-word recognition necessarily involves inaccurate perception by the L2 listeners, or can also arise from interference from L1 phonology at an abstract level, independent of the listeners’ phonetic processing abilities. Results suggest that spurious activation of L2 words containing L2-specific contrasts in spoken-word recognition is contingent on the L2 listeners’ inadequate phonetic processing abilities.

Can hyper-synchrony in meditation lead to seizures? Similarities in meditative and epileptic brain states

Meditation is used worldwide by millions of people for relaxation and stress relief. Given sufficient practice, meditators may also experience a variety of altered states of consciousness. These states can lead to a variety of unusual experiences, including physical, emotional and psychic disturbances. This paper highlights the correspondences between brain states associated with these experiences and the symptoms and neurophysiology of epileptic simple partial seizures. Seizures, like meditation practice, can result in both positive and negative experiences. The neurophysiology and chemistry underlying simple partial seizures are characterised by a high degree of excitability and high levels of neuronal synchrony in gamma-band brain activity. Following a survey of the literature that shows that meditation practice is also linked to high power gamma activity, an account of how meditation could cause such activity is provided. This paper discusses the diagnostic challenges for the claim that meditation practices lead to brain states similar to those found in epileptic seizures, and seeks to develop our understanding of the range of pathological and non-pathological states that result from a hyper-excited and hyper-synchronous brain.